The present invention relates to a transport device with linear motor drive.
Transport devices of this type have already been known for a long time and offer the advantage that the carriages or conveyor elements moved by the linear motor drive can be moved independently of each other, which results in considerable advantages over conventional mechanical transport devices.
One of the purposes served by these types of transport devices is to be found in, for example, the loading of packaging machines with products as known from U.S. Pat. No. 6,876,896 B1, for example, or from U.S. Pat. No. 5,225,725. In these cases, movable conveyor elements or carriages, each equipped with permanent magnets, are moved along a stationary, endless guide rail. The carriages are driven by means of stationary coils, arranged next to one another in a row, each of which is supplied individually with current, as a result of which local magnetic fields are created, which in turn generate a flow of force between the coils and the permanent magnets. By supplying current intelligently to the individual coils, a moving magnetic field can be generated, which can move each individual carriage independently of any of the other carriages which may be present. Because the guide rail is configured as a closed, endless circuit, problems occur particularly in the area of the curved sections as a result of the high frictional and inertial forces of the running rollers on the guide rail and as a result of the partly present play between the running rollers and the guide rail.
To arrive at an improvement here, a transport device has been proposed in WO 2010/086060 A1, in which each carriage is equipped with at least four running rollers, which are intended to ensure the solid support of the carriage on the guide rail without play. The rotational axes of three running rollers are arranged to be perpendicular to the plane defined by the movement of the carriage, whereas the rotational axis of the fourth running roller is parallel to this plane. All of the running rollers travel along guide surfaces which are configured in an internal recess in the guide rail.